The mechanism of tumorigenesis by a bacterium, Agrobacterium tumefaciens, will be investigated. The role of the bacterial plasmid DNA sequences found in bacteria-free tumor cells in tumor formation and maintenance will be studied using tissue culture cells. BIBLIOGRAPHIC REFERENCES: G.E. Klein, P. Jemison, R.A. Haak, and A.G. Matthysse, Physical Evidence of a Plasmid in Rhizobium japonicum, Experientia 31, 532 (1975). A.G. Matthysse and A.J. Stump, The presence of Agrobacterium tumefaciens plasmid DNA in crown gall tumor cells. J. Gen. Microbiol. 95, 9 (1976).